Gosh, this is such a personal thing. I forgo testing because I was not influenced about the pregnancy, I wanted it regardless. I wanted to be stress free and knew we'd handle whatever came (other than basic ultrasounds). There are so many false positives. I was an older mom and was taking my risks. So your 5th month scan was fine? No issues? And because of the early scan results, the doctor is requesting amnio? I could see NOT doing that but don't know what the feelings of your wife and you are. It's now September. I would LOVE an update to hear what you decided and what the results were if you did it.
From what I know NIPT gives you the percentage chance to any genetic disorders.. it's not a definitive option. If those test show high chance of such disorders then you do amnio which is quite precise, but nothing is 100% sure. There are false positives all the time, as amnio is 98% precise